1. Technical Field of the Invention
The present invention relates generally to a starter working to start internal combustion engines, and more particularly to a support structure for an armature of a motor of such a starter.
2. Background Art
In recent years, demands for light weight, compact, and low cost structures of automotive starters have been getting severe all the more. In order to reduce the size, starters have become prevalent which are equipped with a high-speed motor and a reduction gear working to reduce the speed of the motor to produce an increased torque output, however, there has been an increasing need for a higher reduction gear ratio. This has resulted in an increase in speed of an armature of the motor up to 20000 rpm or more, thus requiring further improvement in balancing the armature mechanically.
The above, however, conflicts with reduction in manufacturing cost of the starters. The omission of the balancing operation will result in deflection of the armature shaft and vibrations of bearings during rotation of the motor, which leads to a change in air gap in the motor, thus resulting in mechanical and magnetic noises of the motor and wear of the bearings.
In order to avoid the above problems, Japanese Patent First Publication No. 11-117839 (U.S. Pat. No. 6,114,772 assigned to the same assignees as that of this application) teaches installation of two bearings close to an armature shaft of a starter motor to minimize mechanical deflection of the armature shaft. The starter motor, however, has a commutator which results in an increased interval between the bearings, thus encouraging ease of bending of the armature shaft. This requires the need for balancing the armature in a conventional manner, thus resulting in a difficulty in reducing the manufacturing costs.